The study will examine the level of performance and pattern of neuropsychological functions of children following treatment and recovery from Reye's syndrome. Performance will be related to age of onset and severity of the illness as measured by graded clinical-neurological findings. Parents' perceptions of alterations in family functioning, rehabilitation and academic needs will be assessed to provide information for future psychosocial and educational management. All new cases of Reye's syndrome during a three year period will be administered a battery of neuropsychological tests immediately following the acute phase, one year later, and two years later. Siblings will also be given the same battery of tests at the same time, to provide a control for expected levels of intelligence and neuropsychological functions in each family. Parents will be given an individual measure of intelligence at one and two years post-Reye's to further control for the expected level of intellectual functioning. A structured interview with parents will be carried out to assess the patient's premorbid status, social maturity, personality changes, changes in family functioning and perceived rehabilitation needs.